SNCF, France's national railway system, operates Ouigo trains on which low fares are the norm—but you must know how it operates and follow the rules carefully in order to be satisfied with your journey.

The fares can be astonishing: 16€ for a trip that might cost 60€ on a regular TGV train. How do they do it? Here's how:

20% More Passengers

Ouigo trains use modified TGV Duplex trains that hold 20% more passengers in double-decker cars, all 2nd class, with more closely packed 2x2 or 3x1 seating and no food or beverage service. The railroad also operates Ouigo trains twice the number of hours each day as regular TGV trains.

Tickets Sold Only Online

Tickets can only be bought online on the Ouigo website (French only) or on the SNCF website (French, English and other languages), or via the Ouigo smartphone app (Apple App Store or Google Play Store), and must be bought at least 4 hours before departure. Tickets are issued via email four days or more before departure. You must print your own ticket or have it on your smartphone in order to board the train.

Only Backpack + Purse

Your basic fare includes only one piece of luggage with maximum dimensions of 35cm × 55cm × 25cm (13.8 x 21.6 x 9.8 inches)—about the size of a medium-sized backpack or carry-on wheelie/rollaboard bag that would fit into an airplane's overhead compartment; and one smaller item such as a handbag or small computer bag 15cm x 36cm x 27cm (6 x 14 x 10 inches).

To bring additional or larger luggage (such as a larger airline wheelie bag), you must pay a supplemental fee per bag. If you pay the fee when you buy your ticket in advance online, the cost is 5€, but if you pay it when boarding the train, it's 10€.

If this is the case for your chosen train, you should include the cost of getting to these stations in your calculations of total Ouigo trip cost.

Limited Customer Service

Ouigo staff are few and far between, and some of their time is spent servicing the train rather than helping passengers. Off the train, the only way to contact the company with questions or complaints is by a message form on the Ouigo website—no Customer Service booths, phone numbers or even an email address.

No Food or Beverage Service

Bring your own supplies because the train space normally occupied by food and beverage service is used for passengers on Ouigo trains.

Should You Ouigo?

A trip all the way across France for the price of a sandwich and soft drink? It's pretty tempting!

We've done it, and were completely satisfied—but we were prepared.

Here's the checklist to help you make your decision:

1. Departure & Destination

Locate the exact departure and destination stations of the train, then your own door-to-door departure and arrival points, and understand the time and cost to make your complete journey. Compare this amount with what a more convenient TGV or Intercité train might cost. Think also of comfort (although we've found Ouigo trains have quite adequate comfort).

2. Luggage Limits

If you're traveling with only a medium-sized backpack or overhead-bin wheelie/rollaboard bag plus a purse or computer briefcase, you should be fine, but if you have two large backpacks and two bags that would be checked luggage on an airline, or anything larger or additional, calculate the total luggage cost. It could double or even triple your fare!

3. E-Ticket

Will you be able to receive your emailed ticket four days before your journey, and have it on your smartphone, or print it (even if you are at a hotel)?

4. A Successful—Inexpensive!—Trip

We reserved our Ouigo train a month in advance and printed our tickets weeks before leaving home for France, so we were all set when we boarded the Ouigo train at Aéroport Charles-de-Gaulle's Aérogare 2 for Nantes at the western end of the Loire Valley. It was a good trip, and surprisingly inexpensive.